Fish Necropsy Procedure: A Comprehensive Guide

Fish necropsy is a crucial practice in the realm of aquatic animal health. Just as autopsies on land-based animals help diagnose health issues and uncover the causes of death, fish necropsy serves the same purpose for aquatic life.

This comprehensive guide will delve into the intricacies of fish necropsy, emphasizing its significance in maintaining the well-being of aquatic organisms.

What Is Fish Necropsy?

Fish necropsy, also known as a fish autopsy, is the systematic examination of a deceased fish to determine the cause of death and identify any underlying health issues.

It involves a thorough inspection of both external and internal features. Fish necropsy has distinct features compared to necropsies conducted on terrestrial animals.

The aquatic environment presents challenges, such as water contamination and the need for specialized equipment, which we will address in detail.

What is the Primary Purpose of Fish Necropsy?

The primary purpose of fish necropsy can be summarized in points:

• Diagnostic Examination: To investigate and identify the cause of death or health issues in a deceased fish.
• Disease Surveillance: To monitor and detect diseases and abnormalities within fish populations.
• Research and Study: To contribute to scientific knowledge about fish health, ecology, and aquatic ecosystems.
• Aquatic Management: To make informed decisions in aquaculture, fisheries, and environmental conservation based on health assessments.

Preparing for a Fish Necropsy

Gathering Essential Tools and Equipment: Before embarking on a fish necropsy, you must assemble the necessary tools and equipment.

• Surgical Instruments: Scalpel, scissors, forceps, and probe for precise dissection.
• Sterile Containers: For collecting tissue and organ samples.
• Disinfectants: To sterilize equipment and the necropsy area.
• PPE (Personal Protective Equipment): Lab coat, gloves, and eye protection to maintain aseptic conditions.
• Microscope: For detailed examination of tissue samples.
• Measuring Devices: Calipers and rulers for accurate measurements.
• Camera: To document findings.
• Labels and Markers: For sample identification.
• Reference Materials: Fish anatomy diagrams and disease guides.

Creating a Sterile Environment:

Establishing a sterile workspace is crucial to prevent contamination during the necropsy. Follow these steps:

• Clean the Workspace: Remove any debris or clutter from the work area and disinfect all surfaces.
• Prepare a Disinfection Solution: Use an appropriate disinfectant to clean and sterilize equipment, countertops, and tools.
• Maintain Personal Hygiene: Wash hands thoroughly and wear clean, sterile gloves and lab coats.
• Use Sterile Instruments: Autoclave or heat-sterilize surgical instruments, or use single-use disposable tools.

Now that your workspace is ready, proceed with the step-by-step fish necropsy procedure.

Step-by-Step Fish Necropsy Procedure

A fish necropsy is a comprehensive examination that involves several stages:

External Examination

Inspecting External Abnormalities:

1. Place the fish on a clean, non-porous surface.
2. Examine the fish for external abnormalities such as lesions, discoloration, fin damage, or unusual growths.

Collecting Skin and Scale Samples:

1. Carefully collect skin and scale samples using sterile instruments.
2. Place samples in labeled containers for further analysis.

Internal Examination

Opening the Body Cavity:

1. Use a scalpel to make a ventral incision along the midline from the vent to the operculum.
2. Extend the incision toward the pectoral fins and continue up to the throat.

Examining Organs and Tissues:

1. Gently open the body cavity and secure the fish in place.
2. Examine organs and tissues for abnormalities, noting size, color, and texture.
3. Take photographs if necessary.

Sample Collection

Taking Tissue and Organ Samples:

1. Use sterile instruments to collect tissue and organ samples, including liver, kidney, spleen, and gills.
2. Place samples in separate labeled containers.
3. Ensure proper preservation, either by freezing or using appropriate fixatives.

Proper Handling and Preservation:

Handle samples with care to avoid contamination and ensure accurate analysis. Properly label and store samples at the appropriate temperature.

Data Recording and Analysis

Keeping Detailed Records:

1. Record all findings, including external and internal abnormalities, measurements, and sample details.
2. Document observations thoroughly for future reference.

Interpreting Findings:

Consult reference materials and, if needed, seek expert guidance to interpret findings accurately.

Post-Necropsy Procedures

Proper Disposal of Remains: Dispose of fish remains and contaminated materials following local regulations and environmental guidelines.

Cleaning and Sterilizing Equipment: Clean and sterilize all equipment and the workspace to prevent cross-contamination.

Common Pathologies in Fish

Pathologies observed in fish necropsy can provide valuable insights into the health and well-being of fish populations. These pathologies can affect various organs, including the kidney, liver, muscle, stomach, and intestine. Here are some examples of common pathologies in each of these organs:

Kidney:

• Renal Tubular Necrosis: Damage to the renal tubules, often caused by exposure to toxins or pollutants.
• Fungal Granuloma
• Kidney Inflammation: Inflammatory responses due to infections or immune reactions can affect kidney function.

Liver:

• Fatty Liver Disease: Accumulation of fat in liver tissue, often linked to poor nutrition or metabolic disorders.
• Liver Necrosis: Necrosis in the liver, typically a response to chronic inflammation or injury.
• Liver Flukes: Infections by liver fluke parasites can cause liver damage and inflammation.

Muscle:

• Muscle Haemorrhage: Muscle haemorrhage or disorders that can lead to degeneration, such as white muscle disease in freshwater fish.
• Parasitic Cysts: Parasite larvae can form cysts within muscle tissue, affecting muscle function.

Stomach:

• Ulcers: Erosions or ulcers in the stomach lining, often associated with stress or dietary factors.
• Parasites: Infections by stomach-dwelling parasites can cause irritation and inflammation.
• Impacted Stomach: Blockage or impaction of the stomach due to ingested foreign objects or excessive indigestible material.

Intestine:

• Enteritis: Inflammation of the intestinal lining, often due to infections, dietary issues, or parasites.
• Intestinal Parasites: Infestations by intestinal parasites can lead to tissue damage and inflammation.
• Intestinal Obstruction: Blockage of the intestine, commonly caused by foreign bodies or tumors.

Necropsy Ethics and Regulations

Ethical Considerations in Fish Necropsy: Adhere to ethical principles by minimizing harm to fish and conducting necropsies responsibly.

Compliance with Legal Requirements: Understand and follow local regulations and permit requirements for fish necropsy.

What are the Key Differences Between Fish Necropsy and Fish Autopsy?

Aspect	Fish Necropsy	Fish Autopsy
Purpose	Post-mortem examination of a fish to investigate its health, determine the cause of death, and identify diseases or abnormalities.	Post-mortem examination of a fish with a focus on identifying the cause of death, typically in a clinical or forensic context.
Context	Often performed in aquatic research, fisheries management, and veterinary studies to understand fish health and ecosystems	Frequently associated with criminal investigations, such as illegal fishing, pollution, or suspicious deaths.
Sample Collection	Involves collecting tissue and organ samples for further analysis and research.	May collect samples for forensic purposes but often less focused on research and ecological concerns.
Expertise and Application	Conducted by aquatic veterinarians, biologists, and researchers to study fish populations, diseases, and ecosystem health.	Typically conducted by forensic pathologists, medical examiners, or legal authorities to determine the cause of death for legal or investigative purposes.
Regulatory Considerations	Subject to research and conservation regulations, with permits often required for scientific purposes.	May involve legal and law enforcement agencies, adhering to forensic investigation protocols and regulations.

Frequently Asked Questions (FAQs):

References

• Yanong, R. P. (2003, April). Necropsy techniques for fish. In Seminars in avian and exotic pet medicine (Vol. 12, No. 2, pp. 89-105). WB Saunders.
• Fisher, J. P., & Myers, M. S. (2000). Fish necropsy. In The Laboratory Fish (pp. 543-556). Academic Press.
• Reimschuessel, R., May, E. B., Bennett, R. O., & Lipsky, M. M. (1988). Necropsy examination of fish. Veterinary Clinics of North America: Small Animal Practice, 18(2), 427-433.
• Weber 3rd, E. P., & Govett, P. (2009). Parasitology and necropsy of fish. Compendium (Yardley, PA), 31(2), E12-E12.
• Blazer, V. S., Walsh, H. L., Braham, R. P., & Smith, C. (2018). Necropsy-based wild fish health assessment. JoVE (Journal of Visualized Experiments), (139), e57946.
• Meyers, T. R. (2009). Standard necropsy procedures for finfish. NWFHS Laboratory Procedures Manual. 5th ed. Washington: US Fish and Wildlife Service. p, 64-74.
• Kane, A. S., Baya, A., Reimschuessel, R., St Pe, K. M., Poukish, C. A., & Driscoll, C. P. (1999). Field sampling and necropsy examination of fish. Virginia journal of science, 50(4), 345-364.